I converted a dry tailpipe system to wet by drilling a two 3/16th holes at the tip of the inner pipe on the tail to allow water to flow into the muffler to kill the noise and keep my CMI mufflers from turning to crude. I was at less then 90 db with twin 1000 hp engines at idle. Other mufflers I tested were as high as 105db. The boat was 110 db with dry open exhaust. It would scare poeple when I started it if they were not aware.

The best setup is get the exhaust to exit under water at idle. I am 80 db with my twin 1400 hp cat at idle with CMI downturns.

You drilled the holes just before the mufflers? Which CMI's were they?

The problem I'm watching in Michigan is similar to the problem in Wisconsin, but with an added potential problem. They are looking to change to match Wisconsin law, (with the drive-by test), but tring to get the "Noise Gun" approved for use instead of having to do the drive-by.

If this is approved, they can ticket you from hundreds of feet away for exceeding the maximum db.

I am looking at the new Merc system they developed for Europe, looked closely at SaxMan's pics on his BT, and thinking maybe an in-line muffler, before a turndown underwater, may be the final solution.